How To Get Ready For XHTML?

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XHTML Interview Questions and Answers

5. How To Get Ready For XHTML?

XHTML is not very different from HTML 4.01, so bringing your code up to the 4.01 standard is a good start. In addition, you should start NOW to write your HTML code in lowercase letters.

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The Most Important Differences:

* XHTML elements must be properly nested
* XHTML documents must be well-formed
* Tag names must be in lowercase
* All XHTML elements must be closed


1. Elements Must Be Properly Nested: 

In HTML some elements can be improperly 
nested within each other like this:

<b><i>This text is bold and italic</b></i>

In XHTML all elements must be properly nested 
within each other like this:

<b><i>This text is bold and italic</i></b>

Note: A common mistake in nested lists, is to forget 
that the inside list must be within a li element, like this:

<ul>
  <li>Coffee</li>
  <li>Tea
    <ul>
     <li>Black tea</li>
      <li>Green tea</li>
    </ul>
  <li>Milk</li>
</ul>

This is correct:

<ul>
  <li>Coffee</li>
  <li>Tea
    <ul>
      <li>Black tea</li>
      <li>Green tea</li>
    </ul>
  </li>
 <li>Milk</li>
</ul>

Notice that we have inserted a </li> tag after the
 </ul> tag in the "correct" code example.
Documents Must Be Well-formed

All XHTML elements must be nested within the <html> 
root element. All other elements can have sub (children) 
elements. Sub elements must be in pairs and correctly nested 
within their parent element. The basic document structure is:

<html>
<head> ... </head>
<body> ... </body>
</html>


2. Tag Names Must Be In Lower Case

This is because XHTML documents are XML applications.
XML is case-sensitive. Tags like <br> and <BR> 
are interpreted as different tags.

This is wrong:

<BODY>
<This is a paragraph</P>
</BODY>

This is correct:

<body>
<p>This is a paragraph</p>
</body>


3. All XHTML Elements Must Be Closed

Non-empty elements must have an end tag.

This is wrong:

<p>This is a paragraph
<p>This is another paragraph

This is correct:

<p>This is a paragraph</p>
<p>This is another paragraph</p>


Empty Elements Must Also Be Closed

Empty elements must either have an 
end tag or the start tag must end with />.

This is wrong:

This is a break<br>
Here comes a horizontal rule:<hr>
Here's an image <img src="happy.gif" alt="Happy face">

This is correct:

This is a break<br />

Here comes a horizontal rule:<hr />

Here's an image <img src="happy.gif" alt="Happy face" />


IMPORTANT Compatibility Note:

To make your XHTML compatible with today's browsers, you should add an extra space before the "/" symbol like this: <br  />, and this: <hr  />.

(Continued on next question...)